Subsoils are the greatest storehouses for carbon, as well as one of the most important sources of carbon dioxide in the atmosphere. Global warming is speeding up the decomposition of soil humus. It is also having an effect on the waxy compounds which help plants store carbon in their leaves according to a new study.
About a quarter of the world’s carbon emissions are sequestered by forests, grasslands and pasture land. Plants facilitate photosynthesis to store carbon in their cell walls and in the soil. Close to half the carbon in soil is located in the deeper layers, more than 20 centimeters deep. However, even these layers are heating up due to climate change.
The warming climate is causing substantial loss of the organic compounds that help plants store carbon in their leaves and roots. Up until now, scientists had assumed that complex polymers, which have a more stable molecular structure, were able to withstand natural decomposition for longer and thus store more carbon in the soil.
However, the University of Zurich led study has now shown that the compound lignin, which gives plants their stiffness, was reduced by 17%, while waxy compounds called cutin and suberin, which protect plants from pathogens and are found in leaves, stems and roots, were 30% less. Even pyrongenic carbon, which is the organic compound that remains after a forest fire, was present in significantly reduced amounts.
The experiments were conducted in the forests of the Sierra Nevada in California. The one-meter deep soil was artificially heated up by 4 degees Celsius over a time span of 4.5 years, following daily and seasonal cycles. This amount of warming is in line with projections through the end of the century.
This research has major significance for one of the key strategies in the fight against global warming, namely relying on soils and forests as natural carbon sinks. As part of this strategy, crop plants with especially deep roots and cork-rich biomass are being developed. “Until now it was assumed that this would keep CO2 locked in the ground,” says author of the study Michael W. Schmidt.
“But our results show that all the constituents of soil humus will decrease at the same rate, simple chemical compounds and polymers alike. If these initial observations are confirmed in longer-term field experiments, the consequences are alarming.” If the forest floor loses humus on a large scale and carbon is thus released as CO2, the pace of global warming will be accelerated even more. “Our goal must be to stop emissions at the source,” says Schmidt.
https://phys.org/news/2023-06-climate-carbon-stocks-deep-underground.html